Neutralized amplifier



July 16, 1940. B. EICHHOLZ NEUTRALIZED AMPLIFIER Filed Dec. 1, 1957 INVENTOR BRUNO F/C/l/IOZZ BY k ATTORNEY Patented July 16, 1940 UNITED STATES PATENT OFFICE NEUTRALIZED AMPLIFIER tion of Germany Application December 1, 1937, Serial No. 177,425 In Germany December 8, 1936 Claims.

This invention concerns an arrangement adapted to neutralize radio frequency amplifiers and involves simple means to neutralize under conditions independent of wavelength by means 5 of a difierential condenser utilizing natural stray capacitance.

More in detail this invention is concerned with means designed to neutralize radio frequency amplifiers, especially in short-wave transmitters of m high power. For the purpose of insuring complete neutralization it is known in the art to neutralize not only the plate-to-grid capacitance of the radio frequency tube, but also the other tube capacitances, and in addition also the tube inductances. To this end it is possible, for neutralization to employ a complete mechanical equivalent of the tube without the glass bulb in which exact balance or equalization is effected by a subsequent mechanical change of the constitucuts of the equivalent scheme. It is also known in the art to insure neutralization by an unheated tube of like radio frequency characteristics, though such a tube has the drawback that there is no chance for fine adjustments at a later time.

However, since the tubes are never the same as a result of irregularities in production, such re-adjustment or trimming, most particularly of the grid-plate capacitance, is an absolute necessity.

In describing my invention reference will be 80 made to the attached drawings wherein Figures 1, 2, and 3 each show modified forms of neutralized tube circuit arranged in accordance with my invention.

According to the invention, the plates of the radio frequency amplifier tube R and of the equivalent, or simulation, tube or unheated tube N are connected with two stators 2 and 4 of a differential condenser, the third plate 6 of which is united with the grids of the tubes as shown in Figure 1. To be sure, this scheme somewhat raises the plate-to-grid capacities, though this happens at the expense of the direct stray capacities between the tube plates with the consequence that the resultant oscillation-circuit capacity is not increased by this step. It is then possible to make the grid-to-plate capacities exactly alike by adjustment of the third condenser element 6.

One special embodiment of the basic idea of the invention is illustrated in Figure 2 wherein tube R, which is the same as tube R in Figure 1, is the radio frequency tube with cylindrical plate or anode A, the grid connection G and the cathode K. N is a similar, but unheated tube comprising electrodes An, GN, and KN. The grids are connected with each other and with a metal part D which is capable of reciprocating between the two plates Aand AN. The anodes themselves serve as plates of the differential condenser which is thus formed, on the one hand, by the capacity D AN and, on the other hand, by the capacity DA. By fine adjustment of the metal part D which corresponds to element 6 of Figure 1, any desired accuracy in neutralization is obtainable.

According to another object of the invention,

the increase in capacity is utilized to advantage 10- by virtue of the fact that the fine adjusting means occasions an increase in the plate-to-filament capacitance which in many instances is desirable.

In this exemplified embodiment as shown in 15 Figure 3, the part of the differential condenser D associated with the grids is fixedly arranged, while the capacity distribution upon both sides is insured by shiftable grounded shielding walls J provided upon both sides of part D. The cathodes 20 K and KN are connected together and to ground as is J.

The two shielding means J may advantageously be coupled mechanically by designing them in such a way that they may be shifted to and fro 25 shutter-like, so that reduction of the shielding shielding surface upon the other, and thus a change in the capacity relations.

Details of construction of the differential condenser as here disclosed will be governed by the so particular tubes that are used, and more particularly the shape of the anodes or plates of these tubes, the distance of the tubes from each other, and other constructional details of the scheme. In the majority of instances, it will be favorable to use for the stators of the differential condenser two parallel metal plates connected with the anodes between which a third plate of metal united with both grids is so disposed as to be capable of a to-and-fro movement or is fixedly mounted, as 40 in the second exemplified embodiment above described and furnished, for instance, with shiftable grounded shielding or screening plates.

It is also expedient to make arrangements so that fine adjustment, say, by the aid of a setting 45 knob, may be efiected continuously so that the degree of neutralization may at all times be reset to a maximum value.

I claim:

1. In an arrangement adapted to the neutrali- 50 zation of an electron discharge tube used as an alternating current amplifier, said tube having grid and anode electrodes, a first capacity substantially equivalent to the capacity between the anode and grid of said discharge tube, a differ 55 ential condenser having two stators and a movable element, means coupling the stators of said condenser, one to the anode of the amplifier tube and the other to an element of the said capacity and means coupling the movable element of said condenser to the grid of the tube and to the other element of said capacity.

2. In a high frequency system, an electron discharge tube having an anode, and a control grid, and means for connecting said tube in a high frequency circuit and neutralizing the circuit without disturbing the resonant frequency thereof by said neutralization comprising a second tube having two electrodes between which capacity exists, substantially equal to'the capacity to be neutralized between the two electrodes of the first tube, a resonant circuit connecting an electrode in said first tube to an electrode of said second tube, said resonant circuit including the capacity between the so connected electrodes, and a movable element connected. to the other of the electrodes in each of said tubes and mounted for equaland opposite movement between said two electrodes connected by said resonant circuit to supplement the capacity between said two electrodes of said tubes.

3. In an arrangement adapted to neutralize an electron discharge tube used as an alternating current relay, said tube having grid and anode electrodes, a capacity in the form of an additionel tube with anode and grid electrodes having' inherent capacity therebetween substantially equivalent to the capacity between the anode and grid of said discharge tube, a differential condenser having two stator plates formed by the anode electrodes of said discharge tube and said tube comprising said first capacity, said differential condenser also comprising a movable element capacitively related to said anodes and mounted for movement relative thereto, and means connecting said movable element of said differential condenser to the grid electrodes of said d scharge tube and said tube of said first capacity.

4. In an arrangement for neutralizing an electron discharge tube connected in an alternating current relaying circuit, said tube having a grid and an anode and a cathode, a first capacity, comprising an additional tube having anode and grid electrodes with capacity therebetween substantially equivalent to the capacity between the anode and grid of said discharge tube, said additional tube having a cathode, a difierential condenser having two stators formed by the anodes of said tubes, and an additional member fixed between said anodes and capacitively coupled thereto, a connection'between said additional member and the grids of said tubes and a movable member located between each of said anodes and said additional member and a connection between said movable member and the cathodes of said tubes. 5. An arrangement as recited in claim 8 wherein' said movable members between said anodes and saidadditional member are simultaneously movable in directions to decrease the capacity in the condenser formed by one of said anodes and simultaneously increase the capacity in the condenser formed by the other of said anodes.

:BRUNO EICHHOLZ. 

